This application claims the priority of German patent document 100 12 833.5, filed Mar. 16, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a motor vehicle having a transmission controlled by an electronic transmission unit and an internal-combustion engine controlled by an electronic engine unit.
The transmission unit and the engine unit can be combined in one control unit or can consist of two separate control units. In each case, a communication connectionxe2x80x94in the case of two separate control units, particularly in the form of a digital data bus (for example, a CAN bus)xe2x80x94is provided between the transmission unit and the engine unit. Conventionally, the transmission unit, normally as a function of a gear selection switch, shifts the selected gear by controlling actuators in the transmission. Here, the term xe2x80x9cgear selection switchxe2x80x9d is to be understood in the widest sense, specifically, for example, as a selector switch for a driving position in the case of a (semi) automatic manual transmission (1st gear, 2nd gear . . . , reverse gear, neutral position) as well as a selector switch for a driving position (P, R, N, D . . . ) in the case of an automatic transmission.
In new electronically controlled transmissions, currently, a mechanical connection is no longer provided between the electrical or electronic gear selection switch and the transmission. Rather, a purely electrical signal communication takes place between the gear selection switch and the transmission unit. Thus, in the event of a defect of the gear selection switch or an interruption of the signal transmission line between the gear selection switch and the transmission unit, the adjustment of the gear selection switch can no longer be recognized. The transmission unit will then control the transmission in an emergency operation in which, under certain circumstances, the selected gear (the selected position) is simply maintained. As a result, a change of the driving direction which might simply be desired by the driver would not be implemented.
Furthermore, the transmission control unit itself may be defective, so that the selected gear, corresponding to the adjustment of the gear selection switch, cannot be shifted in the transmission by means of the transmission control unit. When the transmission unit fails completely, so-called mechanical emergency operation takes place in which, also under certain circumstances, the selected gear (the selected position) is maintained, and an intended change of driving direction is not implemented.
In such emergency operation situations, it is also known to warn the driver by corresponding feedback. (Compare, for example, German Patent Document DE 198 10 479 A1.) However, it is possible that in particular cases the driver may overlook or not hear this feedback.
It is an object of the invention to increase the degree of safety in a vehicle such as described above, especially with regard to the above-described emergency operation situation.
This and other objects and advantages are achieved by the control system according to the invention, in which the engine unit imposes a limitation on the acceleration of the vehicle upon the occurrence of an emergency that can be detected by way of the communication connection, including a situation in which the adjustment of the gear selection switch is not recognized by the transmission unit and/or the selected gear cannot be shifted in the transmission. The term xe2x80x9cgearxe2x80x9d can be a particular reverse or forward gear (R-gear or, for example, 1st gear) as well as a reverse or forward driving position (xe2x80x9cRxe2x80x9d or, for example, xe2x80x9cDxe2x80x9d)
The emergency is preferably detected by the engine unit when the transmission unit actively emits a corresponding emergency signal to the communication connection. Alternatively, or in addition, the emergency can be detected by the engine unit when the transmission unit emits no signals, or implausible signals to the communication connection.
In the case of the first alternative, it is more likely that a defect that can be detected by the transmission unit exists in the gear selection switch or in the signal transmission line between the gear selection switch and the transmission unit. In this case, the transmission unit can activate a defined emergency operation, for example, holding the gear which was engaged before the defect. In such a case, the transmission unit knows which gear is engaged, and the actively emitted emergency signal could be emitted only when and as long as a reverse or forward gear is actually held. However, if the defined emergency operation activates the engagement of the neutral position, the emission of an emergency signal is not absolutely necessary in order to trigger the limiting function according to the invention in the engine unit, because it would have no effect in the neutral position.
In the second embodiment, there is more of a total failure of the transmission unit. In this case, the engine unit must assume the worst case and carry out the limiting function itself. Particularly by limiting the torque of the internal-combustion engine, the limitation of the acceleration is carried out as a function of the time, the vehicle path and/or its speed.
The limiting function according to the invention is preferably begun during the start of the drive or at a speed below a very low threshold value.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.